tomcon
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If charge tapers near the end, why doesn't watts/amps draw drop?

Mon Jan 07, 2019 11:00 pm

I am charging my new 2018 Leaf at 120V. have a plug-in meter that plugs into the wall plug and then the charger is plugged into the meter. When i start charging, it reads about 12A and about 1150 Watts draw. Right near the end of charging to 100%, like the hour or two before the charger goes off, it is still reading the same Amps and Watts. I had expected those to drop near the end, since it seems like you are not charging the battery as much near the end (tapering) and so why is it drawing the same power? Like in the old days when you charged a 12V battery you could see the Amps drop to near 0 at the end, and then you knew charging was done. Whey doesn't charging the Leaf battery have the same behavior? Thanks, if you understand this issue and can reply!

LeftieBiker
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Re: If charge tapers near the end, why doesn't watts/amps draw drop?

Mon Jan 07, 2019 11:02 pm

When you charge at 120 volts (L-1) you are already charging at a low rate. There is no need to taper this charge down because it is already using a slow charge rate. At the very end, when all three charge lights are lit solid blue, you might see fluctuations as the pack equalizes.
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Nubo
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Re: If charge tapers near the end, why doesn't watts/amps draw drop?

Mon Jan 07, 2019 11:29 pm

LeftieBiker wrote:When you charge at 120 volts (L-1) you are already charging at a low rate. There is no need to taper this charge down because it is already using a slow charge rate. At the very end, when all three charge lights are lit solid blue, you might see fluctuations as the pack equalizes.


+1. For a 2018, Level 1 is a trickle charge to begin with.

Not sure about the readings. 12A @ 120V should be closer to 1440W 1150W would indicate a voltage sag to 95V. That is extreme and would indicate some serious problems with the wiring. Or hopefully it's just the meter that is faulty.
I noticed you're still working with polymers.

alozzy
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Re: If charge tapers near the end, why doesn't watts/amps draw drop?

Mon Jan 07, 2019 11:32 pm

To add to what LeftieBiker said, and relating to your other post, your 2018 LEAF would charge at up to a 6.6 kw (240v x 27.5A) rate (obviously, that doesn't account for losses, which are less for L2 charging). If charging on an L2 EVSE, you would see that at around 85% SOC, the rate would steadily taper between 85% SOC and 100% SOC.

Of course, if you follow what seems to be best practices then you would only occasionally charge to 100% (when you need it) and most of the time charge to 80% SOC. In that case, you should see very little tapering when charging with L2 (ie you should see a 6 kW or more charging rate for the entire charge cycle)
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tomcon
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Re: If charge tapers near the end, why doesn't watts/amps draw drop?

Tue Jan 08, 2019 12:06 am

Thanks Nubo, yes, i erred, it was about 1350 watts, and more exact on the Amps i think is about 11.5 (I had rounded to 12).

I keep hearing not to charge to 100%...from everybody here, but not Nissan! But, i think i shall try it, though they make it inconvenient. What do people do, take the cars estimate for time to full charge and subtract a few hours, and then set the timer? And the purpose of that is just battery longevity, that is improved if not fully charged? Does anybody know of an estimate for effect on longevity, say, if you charge only to 80% all the time instead of 100% all the time? An extra year? (If so, not insignificant!). I currently charge to 100% (for convenience/simplicity), but not every night, only if i've used enough to drop below about 70% or so. So, i don't charge to 100% every night, but i do charge to that if i charge at all.

Had the car just 2 months. Trying to get my rhythm/technique down!

Thanks!

alozzy
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Re: If charge tapers near the end, why doesn't watts/amps draw drop?

Tue Jan 08, 2019 12:17 am

The "evidence" is mostly anecdotal, but it's actually more important to not leave the pack sitting at 100% SOC for hours, particularly when ambient temperature is high. As long as you are driving shortly after the pack reaches 100% SOC, and only charge to 100% SOC when it's not hot outside, then you are very likely not going to see any worse degradation.

The combination of high temps, a high state of charge for long periods of time, and in particular rapid charging under those conditions will definitely impact the life of the battery pack and cause premature degradation.
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SageBrush
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Re: If charge tapers near the end, why doesn't watts/amps draw drop?

Tue Jan 08, 2019 6:35 am

alozzy wrote:The "evidence" is mostly anecdotal, but it's actually more important to not leave the pack sitting at 100% SOC for hours, particularly when ambient temperature is high. As long as you are driving shortly after the pack reaches 100% SOC, and only charge to 100% SOC when it's not hot outside, then you are very likely not going to see any worse degradation.

The combination of high temps, a high state of charge for long periods of time, and in particular rapid charging under those conditions will definitely impact the life of the battery pack and cause premature degradation.


1+
The only thing I add to that is to avoid charging a hot battery if possible. My routine is to start charging around 3am in the summer. This gives the battery some hours of cool air at night to first cool down and keeps the time the battery is at high SoC down. It is also simple and convenient, and I do not have to fiddle with calculated stop charge times. My routine is with an L2 EVSE and a 6.6 kW max rated OBC
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11/2018: 56.16 Ahr, 30k miles
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tomcon
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Re: If charge tapers near the end, why doesn't watts/amps draw drop?

Tue Jan 08, 2019 11:33 pm

Thanks for all the great thoughts. I'd still like to actually observe the taper at the end of a charge if i could. Just for the fun of it.

As for charge habits. I rarely have the fully charged car sit very long, even if i charge to full, i'm still going to use it sometime that day. So, i think i'll go with, maybe 9 months a year (except summer), i'll do what i'm doing now, charge overnight to full, if i'm below 70% and not at all if i'm still above 70%. At 110V if i'm below 70% we're still talking at least 10-11 hours to full charge anyway. In the summer i like the idea of not starting the charge until later to give the battery some time to cool, and maybe i'll try to cut it off a little before 100% if i can estimate it. Unless of course i specifically need longer range the next day.

Overall, though, its a really fun machine and i really like it. Thanks for all the getting-started help.

Dooglas
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Re: If charge tapers near the end, why doesn't watts/amps draw drop?

Wed Jan 09, 2019 12:25 am

It would be helpful for you to post your location with your information to the left of your post (i.e. in your profile). In a discussion like this, charging practices are strongly influenced by the seasonal climate where your vehicle is located. The issue of capacity loss related to charging practices mostly seems to be linked to battery pack temperatures.
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cwerdna
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Re: If charge tapers near the end, why doesn't watts/amps draw drop?

Wed Jan 09, 2019 12:58 am

Dooglas wrote:It would be helpful for you to post your location with your information to the left of your post (i.e. in your profile). In a discussion like this, charging practices are strongly influenced by the seasonal climate where your vehicle is located. The issue of capacity loss related to charging practices mostly seems to be linked to battery pack temperatures.

If asked that the location field be mandatory many times. It hasn't happened. :(

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